The invention relates to a spark ignited internal combustion engine with at least one cylinder that accommodates a reciprocating piston, with a cylinder head that receives at least one ignition device per cylinder and in which are formed one exhaust and two intake manifolds, said exhaust manifold communicating with a combustion chamber by way of an exhaust port and said intake manifolds communicating therewith by way of intake ports, said exhaust port being controlled via an exhaust valve and said intake ports via intake valves, said exhaust port on the one hand and said intake ports on the other hand being arranged to different sides of an elevated plane of the engine that passes through the axis of the cylinder and through the axis of the crankshaft, said intake manifolds being at least in sections arranged substantially in the direction of the cylinder""s axis and being formed in such a manner that a reverse tumble flow is initiated in the combustion chamber, said flow being oriented from the intake ports toward the piston and from there toward the exhaust port.
An internal combustion engine with two intake manifolds and one exhaust manifold is described in U.S. Pat. No. 5,305,720, the intake manifolds initiating a reverse tumble flow in the combustion chamber. Particularly on lean operation, carburetion, combustion and scavenging of the combustion chamber may be improved by virtue of this reverse tumble flow. However, the ignition device, which is arranged in the region of the cylinder""s axis and projects into the combustion chamber occasions relatively high flow losses as the ignition device is positioned in a region of high flow velocities. In three-valve internal combustion engines with tumble flow in particular, the central positioning, which offers itself, of the ignition device is inconvenient on account of the high flow velocities prevailing therein and of the adverse combustion initiation.
The GB 2 310 003 A describes an internal combustion engine with reverse tumble flow with four valves per cylinder in which the ignition device discharges slantways between the valves in a central region of the combustion chamber.
The JP 08-246877 A also discloses an internal combustion engine with four valves and one central spark plug. Here too, high flow velocities may be observed in the region of the ignition device.
The JP 04-136417 A indicates an internal combustion engine with reverse tumble flow with three intake and two exhaust valves and with several ignition devices per cylinder. The ignition devices are each arranged in a central region between two valves. The high flow velocities and the strong turbulences prevailing in the region of the ignition devices do not permit to guarantee a uniform combustion of the mixture.
The publications EP 0 178 663 A2 and DE 28 54 332 A1 describe internal combustion engines with two intake valves and one exhaust valve per cylinder in which a swirl flow is produced around the cylinder""s axis by means of one main and one auxiliary intake manifold. The ignition device is arranged in a region with medium swirl flow that is located near the intake. This idea cannot be used for internal combustion engines with reverse tumble flow in the combustion chamber.
Furthermore, the DE 198 49 913 A1 discloses an internal combustion engine with two intake valves and with one exhaust valve per cylinder. One spark plug is thereby arranged between the intake valve and a respective one of the exhaust valves. In the combustion chamber, there is produced a tumble flow which is oriented from the intake side toward the exhaust side and not a reverse tumble flow that is directed from the intake ports toward the piston and from there toward the exhaust port.
It is the object of the invention to avoid these drawbacks and to reduce the flow losses in an internal combustion engine of the type mentioned herein above in the easiest possible manner.
This is achieved in accordance with the invention by arranging at least one ignition device in the cylinder head bottom to the side thereof in the region of the cylinder wall. The ignition device thereby discharges into the combustion chamber at a non-critical location of the cylinder head ceiling where the reverse tumble flow produces relatively low flow velocities.
Preferably, at least one ignition device is arranged in the region of the elevated plane of the engine. In the region of the elevated plane of the engine there is enough space for arranging the ignition device laterally so that there are hardly any constructional restraints. Furthermore, the lateral arrangement of the ignition device has the advantage that intake and exhaust ports may be devised with larger dimensions than in an ignition device that is centrally arranged.
A particularly good combustion initiation can be achieved when at least two ignition devices are arranged in the cylinder head bottom on either side of a transverse plane of the engine that includes the cylinder""s axis and is oriented normal to the elevated plane of the engine. The arrangement of the three valves in the cylinder head has the advantage of offering enough space for two ignition devices as well. In a particularly preferred embodiment, the ignition devices may thereby be arranged symmetrically about the transverse plane of the engine. The intake ports and the exhaust port too may be arranged symmetrically about the transverse plane of the engine.
In another variant in accordance with the invention there are provided three ignition devices in the cylinder head bottom, a first ignition device being arranged between the two intake ports, a second ignition device between the one intake port and the exhaust port and a third ignition device between the other intake port and the exhaust port. The three ignition devices thereby discharge into the combustion chamber at non-critical locations of the cylinder head ceiling where the reverse tumble flow produces relatively low flow velocities. The three ignition devices permit to achieve a uniform combustion of the fuel-air mixture in the combustion chamber.
The second and the third ignition devices are preferably arranged in the region of the elevated plane of the engine. In the region of the elevated plane of the engine there is enough space for arranging the ignition device laterally so that there are hardly any constructional restraints. Furthermore, the lateral arrangement of the ignition device has the advantage that intake and exhaust ports may be devised with larger dimensions than in an ignition device that is centrally arranged.
A particularly good combustion initiation can be achieved when the second and the third ignition devices are arranged in the cylinder head bottom to either side of a transverse plane of the engine that includes the cylinder""s axis and is oriented normal to the elevated plane of the engine. The arrangement of the three valves in the cylinder head has the advantage of offering enough space for three ignition devices as well. In a particularly preferred embodiment, the ignition devices may thereby be arranged symmetrically about the transverse plane of the engine. The intake ports and the exhaust port too may be arranged symmetrically about the transverse plane of the engine.
To dispense with one component part in the region of the cylinder""s axis furthermore has the advantage that the intake manifolds may be optimally adapted to produce the reverse tumble flow. To have at least one intake manifold crossing the elevated plane of the engine is of particular advantage.
In a particularly preferred variant of the invention the intake manifolds are arrangedxe2x80x94in horizontal projectionxe2x80x94between at least one lever axis of the intake valve and one lever axis of the exhaust valve. This permits on the one hand to optimally form the reverse tumble flow and on the other hand to offer enough space for the ignition devices. Furthermore, there may also provided that six cylinder head bolts for fastening the cylinder head on the cylinder housing are arranged with rotational symmetry about the cylinder. By virtue of the intake manifolds that are arranged in the direction of the cylinder""s axis, the cylinder head bolts may be arranged at regular intervals around the circumference of the cylinder without any constructional restraints arising with regard to the design of the intake manifolds or of the cylinder head. By having the cylinder head uniformly pressed against the cylinder housing, high compression ratios may be realized. An internal combustion engine with two swirl producing intake manifolds per cylinder in which each cylinder head is fastened to the cylinder housing by means of six cylinder head bolts forms the subject of the DE 21 46 015 A. The six cylinder bolts provide but little liberty in designing and guiding the manifolds. According to the DE 21 46 015 A, the fastening of the cylinder head by means of six cylinder head bolts per cylinder is mainly made possible by two relatively angled intake flange areas per cylinder which presents the disadvantages that manufacturing is more complicated and that more space is required.
In another embodiment of the invention there is provided that the two intake manifolds start at one common suction channel that is arranged between at least one lever axis of the intake valve and one lever axis of the exhaust valve. For a simple design of the channel the suction channel may advantageously have an oval or a rectangular section with rounded angles.
A device for controlling the intake air is arranged in the suction channel or in the intake manifolds. The device for controlling the intake air may consist of two control flaps that are coupled to one another, one of the two control flaps being provided for each of the intake manifolds. The control flaps are preferably relatively phase-shifted, i.e., one control flap causes one intake manifold to open at an earlier stage than the other.
Alternatively, a rotary slide valve may be arranged in the region where the suction channel branches into the intake manifolds, the axis of rotation of said rotary slide valve being arranged substantially crosswise relative to the suction channel and preferably parallel to the axis of the crankshaft.
Optimal control of the intake air may be achieved when the rotary slide valve is provided with one control port for each intake manifold, the control ports being preferably arranged in such a manner that they are relatively phase-shifted.
In another embodiment of the invention there is provided that an injection device for the semi-direct injection of fuel discharges into at least one intake manifold, preferably into that intake manifold that is opened first by the device for controlling the intake air.
To dispense with one component part in the region of the cylinder""s axis has furthermore the advantage that the intake manifolds may be optimally laid out for producing the reverse tumble flow. It is thereby of particular advantage when at least one intake manifold crosses the elevated plane of the engine.
The fuel may be fed directly into the combustion chamber by way of an injection device that is arranged to the side between the two intake ports.
Alternatively, there may be provided that an injection device for the semi-direct injection of fuel that occurs in synchronism with suction discharges into at least one intake manifold, preferably into that intake manifold that is opened first by the device for controlling the intake air. As compared to the direct fuel injection, this has the advantage that the fuel injection device does not coke and that the fuel may be injected with considerably lower injection pressure.
In a particularly easy to produce variant there is provided that each intake manifold may be formed by and released from a steel mold that is provided with a slope.